From: Simon Martin <simon@nasilyan.com>
Date: Thu, 8 Aug 2024 12:59:49 +0000 (+0200)
Subject: c++: Don't accept multiple enum definitions within template class [PR115806]
X-Git-Tag: basepoints/gcc-16~6698
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=786ebbd6058540b2110da16a693f0c582c11413c;p=thirdparty%2Fgcc.git

c++: Don't accept multiple enum definitions within template class [PR115806]

We have been accepting the following invalid code since revision 557831a91df

=== cut here ===
template <typename T> struct S {
  enum E { a };
  enum E { b };
};
S<int> s;
=== cut here ===

The problem is that start_enum will set OPAQUE_ENUM_P to true even if it
retrieves an existing definition for the enum, which causes the redefinition
check in cp_parser_enum_specifier to be bypassed.

This patch only sets OPAQUE_ENUM_P and ENUM_FIXED_UNDERLYING_TYPE_P when
actually pushing a new tag for the enum.

	PR c++/115806

gcc/cp/ChangeLog:

	* decl.cc (start_enum): Only set OPAQUE_ENUM_P and
	ENUM_FIXED_UNDERLYING_TYPE_P when pushing a new tag.

gcc/testsuite/ChangeLog:

	* g++.dg/parse/enum15.C: New test.
---

diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index a468bfdb7b6..f23b635aec9 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -17059,22 +17059,24 @@ start_enum (tree name, tree enumtype, tree underlying_type,
 	  enumtype = cxx_make_type (ENUMERAL_TYPE);
 	  enumtype = pushtag (name, enumtype);
 
-	  /* std::byte aliases anything.  */
-	  if (enumtype != error_mark_node
-	      && TYPE_CONTEXT (enumtype) == std_node
-	      && !strcmp ("byte", TYPE_NAME_STRING (enumtype)))
-	    TYPE_ALIAS_SET (enumtype) = 0;
+	  if (enumtype != error_mark_node)
+	    {
+	      /* The enum is considered opaque until the opening '{' of the
+		 enumerator list.  */
+	      SET_OPAQUE_ENUM_P (enumtype, true);
+	      ENUM_FIXED_UNDERLYING_TYPE_P (enumtype) = !! underlying_type;
+
+	      /* std::byte aliases anything.  */
+	      if (TYPE_CONTEXT (enumtype) == std_node
+		  && !strcmp ("byte", TYPE_NAME_STRING (enumtype)))
+		TYPE_ALIAS_SET (enumtype) = 0;
+	    }
 	}
       else
 	  enumtype = xref_tag (enum_type, name);
 
       if (enumtype == error_mark_node)
 	return error_mark_node;
-
-      /* The enum is considered opaque until the opening '{' of the
-	 enumerator list.  */
-      SET_OPAQUE_ENUM_P (enumtype, true);
-      ENUM_FIXED_UNDERLYING_TYPE_P (enumtype) = !! underlying_type;
     }
 
   SET_SCOPED_ENUM_P (enumtype, scoped_enum_p);
diff --git a/gcc/testsuite/g++.dg/parse/enum15.C b/gcc/testsuite/g++.dg/parse/enum15.C
new file mode 100644
index 00000000000..d19262156b9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/parse/enum15.C
@@ -0,0 +1,9 @@
+// PR c++/115806
+// { dg-do compile }
+
+template <typename T>
+struct S {
+  enum E { a }; // { dg-note "previous definition" }
+  enum E { b }; // { dg-error "multiple definition" }
+};
+S<int> s;